Nielsen said new security upgrades to the admissions program will help block suspected criminals from entering the United States from ‘high-risk’ countries, the head of the U.S. Department of Homeland Security said on Monday.

‘We will be rolling out new security measures for applicants from high-risk countries which will seek to prevent the program from being exploited by terrorists, criminals and fraudsters,’ Nielsen said at a public event in Washington.

‘These changes will not only improve security but importantly they will help us better assess legitimate refugees fleeing persecution.’